A wheel loader is commonly used to load and move substantial volumes of dirt and like material from one location to another. A conventional wheel loader includes a relatively large frame which is supported for self-propelled movement over land by pairs of air-filled tires and has a bucket or implement mounted to one end thereof. The bucket or implement can be selectively elevated to a position above side panels on a truck or the like and can be selectively tilted to "dump" materials therefrom.
The bucket or implement is typically connected to forward ends of a pair of lift arms extending from and having opposite ends pivotally connected to the frame of the loader. The bucket is connected to the lift arms in a manner allowing tilting movement of the bucket about a generally horizontal axis.
Hydraulic motors generally provide the motive force for moving the bucket or implement. Typically, a pair of hydraulic motors are connected to the frame for pivoting the lift arms and thereby adjusting the elevation of the bucket. Another hydraulic motor tilts the bucket about its horizontal axis to dump the materials from the bucket.
The land or terrain over which the wheel loader moves is typically uneven, and the wheel loader has an unsprung suspension except for the air-filled tires. As the loader is driven, the uneven terrain and the bucket at one end thereof causes a pitching motion to be imparted to the loader. Having the bucket filled as the loader is driven across the field amplifies the pitching problem. The instability or vertical bounce imparted to the loader translates to poor driving comfort and makes steering and general handling conditions difficult. Accordingly, the operator is required to reduce ground speed of the loader thereby adversely effecting productivity.
In an attempt to reduce the pitching motion, some wheel loaders have been known to include a fluid accumulator in combination with the hydraulic motors used to vertically position the bucket relative to the frame. Unexpected vertical displacement of the bucket results, however, when a residual charge in the accumulator does not correspond to the fluid pressure in the hydraulic lift motors upon activation of the accumulator. As will be appreciated, unexpected vertical displacement of the bucket can have serious drawbacks during operation of the loader.
Another problem involved with wheel loaders has been observed when the bucket is tilted to dump materials therefrom. A typical loader has a linkage mechanism which connects the hydraulic dump motor to the bucket. Retracting movement of the dump motor acts to tilt the bucket. During operation, a stop limits the travel of the linkage mechanism thereby limiting tilting action of the bucket. Normally, the stroke of the hydraulic motor used to forcibly tilt the bucket is somewhat greater than the tilt travel of the bucket as limited by the stop. When the linkage mechanism reaches the limit stop, the retracting action of the hydraulic motor acting to tilt the bucket pulls the lift arms downward thereby forcing fluid out of the hydraulic lift motors and into the accumulator.
It is not uncommon for the bucket to fall about 10 inches after the bucket has been moved into its maximum tilt position. As will be appreciated, when the bucket is elevated to dump its load into a truck or the like, a 10 inch drop of the lift arms will likely impact against the side of the truck thereby jolting both the wheel loader and truck along with the operator of such equipment.
Thus, there is a need and a desire for a shock absorbing mechanism operative to absorb vibrations from the bucket thereby reducing the pitching motion and facilitating a smoother ride for the wheel loader over uneven terrain. Another object of the present invention is to inhibit inadvertent vertical displacement of the bucket during operation of the wheel loader.